ISO INTERNATIONAL STANDARD

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1 INTERNATIONAL STANDARD ISO First edition Microbeam analysis Analytical transmission electron microscopy Methods for calibrating image magnification by using reference materials having periodic structures Analyse par microfaisceaux Microscopie électronique en transmission analytique Méthodes d'étalonnage du grandissement d'image au moyen de matériaux de référence de structures périodiques Reference number ISO 2010

2 Provläsningsexemplar / Preview PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat accepts no liability in this area. Adobe is a trademark of Adobe Systems Incorporated. Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below. COPYRIGHT PROTECTED DOCUMENT ISO 2010 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel Fax copyright@iso.org Web Published in Switzerland ii ISO 2010 All rights reserved

3 Contents Page Foreword...iv Introduction...v 1 Scope Normative references Terms, definitions and abbreviated terms Image magnification Definition of the image magnification Expressing magnification Reference materials General Requirements for CRM/RM Storage and handling Calibration procedures General Mounting CRM/RM Setting TEM operating conditions for calibration Capturing digitized image Digitizing the image recorded on photographic film Measurement of the angle-corrected distance D t, from the digitized image Digitization of reference scale for pixel size calibration Calibration of image magnification Calibration of scale bar Calibration procedure for length measurements using photographic film only Accuracy of image magnification Uncertainty of measurement result Calibration report General Contents of calibration report...22 Annex A (informative) Parameters that influence the resultant magnification of a TEM...23 Annex B (normative) Flowchart of image-magnification calibration procedure...24 Annex C (normative) How to decide the number of lines for averaging...25 Annex D (informative) Reference materials for magnification calibration...28 Annex E (informative) Example of test report for calibration of TEM magnification...31 Bibliography...40 ISO 2010 All rights reserved iii

4 Provläsningsexemplar / Preview Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO was prepared by Technical Committee ISO/TC 202, Microbeam analysis, Subcommittee SC 3, Analytical electron microscopy. iv ISO 2010 All rights reserved

5 Introduction The transmission electron microscope is widely used to investigate the micro/nano-structure of a range of important materials such as semiconductors, metals, nano-particles, polymers, ceramics, glass, food and biological materials. This International Standard is relevant to the need for magnification calibration of the images. It describes the requirements for calibration of the image magnification in the transmission electron microscope using a certified reference material or a reference material having periodic structures. ISO 2010 All rights reserved v

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7 INTERNATIONAL STANDARD Microbeam analysis Analytical transmission electron microscopy Methods for calibrating image magnification by using reference materials having periodic structures 1 Scope This International Standard specifies a calibration procedure applicable to images recorded over a wide magnification range in a transmission electron microscope (TEM). The reference materials used for calibration possess a periodic structure, such as a diffraction grating replica, a super-lattice structure of semiconductor or an analysing crystal for X-ray analysis, and a crystal lattice image of carbon, gold or silicon. This International Standard is applicable to the magnification of the TEM image recorded on a photographic film, or an imaging plate, or detected by an image sensor built into a digital camera. This International Standard also refers to the calibration of a scale bar. This International Standard does not apply to the dedicated critical dimension measurement TEM (CD-TEM) and the scanning transmission electron microscope (STEM). 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO Guide 30:1992, Terms and definitions used in connection with reference materials ISO Guide 34:2000, General requirements for the competence of reference material producers ISO Guide 35:2006, Reference materials General and statistical principles for certification ISO/IEC 17025:2005, General requirements for the competence of testing and calibration laboratories ISO/IEC Guide 98-3:2008, Uncertainty of measurement Part 3: Guide to the expression of uncertainty in measurement (GUM:1995) 3 Terms, definitions and abbreviated terms For the purposes of this document, the terms and definitions in ISO Guide 30 and the following apply. 3.1 alignment series of operations to align the incident direction of the electron beam to the optical axis using deflectors and/or mechanical knobs 3.2 beam damage specimen damage generated by irradiation with the electron beam ISO 2010 All rights reserved 1

8 Provläsningsexemplar / Preview 3.3 certified reference material CRM reference material, accompanied by a certificate, one or more of whose property values are certified by a procedure which establishes its traceability to an accurate realization of the unit in which the property values are expressed, and for which each certified value is accompanied by an uncertainty at a stated level of confidence For the purposes of this International Standard, a CRM possesses periodic structure(s), with the desired range of periodic interval and accuracy, to be used for the calibration of the image magnification. 3.4 contamination formation of a deposited layer of any material due to the interaction of the electron beam with the sample and/or its immediate environment 3.5 crystal orientation direction of crystal which is represented by crystal index During TEM imaging, it is often useful to have a crystalline specimen aligned such that a specific (low index) zone axis is parallel, or nearly parallel, to the beam direction (optical axis). 3.6 defocus focusing condition in which the vertical positioning of the specimen is not coincident with the object plane of the objective lens Over-focus condition is that the specimen height is nearer the lens than the object plane, under-focus condition is that the specimen height is further from the lens than the object plane. 3.7 diffraction grating replica shadow-casting carbon replica film constituting a grating which contains 500 to parallel grooves per millimetre, or cross-line grating with a similar line spacing A diffraction grating replica can be used as a reference material for calibration of the image magnification in the low to medium-low magnification range. 3.8 digital camera device that detects the image using a chip-arrayed image sensor, such as a charge-coupled device (CCD) or complementary metal-oxide semiconductor (CMOS), that converts a visual image to an electric signal 3.9 dynamic range range of detectable electron doses illuminated on the detector, in which the image signal can be detected properly 3.10 excitation current electric current applied to the coil of the magnetic lens 3.11 glass scale ruler on which a fine scale is drawn and utilized as the reference scale to measure the distance in the digitized image after digitizing it with an image scanner The transparency and thermal stability of the glass scale are convenient to get the digitized reference image with a transmitted image scanner and to make the contact image on the imaging plate. 2 ISO 2010 All rights reserved

9 3.12 goniometer stage device to move the specimen laterally and vertically, and to tilt the specimen by tilting the specimen holder around the longitudinal holder axis 3.13 horizontal field width HFW original length corresponding to full width in the horizontal direction on a magnified image 3.14 image two-dimensional projection of the specimen structure generated by TEM A photographic film, an imaging plate, and an image sensor built into a digital camera are examples of devices for detecting the image image file format processing method to encode the image information for storage in a computer file 3.16 image magnification ratio of the linear dimension of the specific structure/scaling on the image detector, such as a photographic film, an imaging plate, or an image sensor built into a digital camera, to the corresponding linear dimension of the structure/scaling on the specimen 3.17 imaging plate IP electron image detector consisting of a film with a thin active layer embedded with specifically designed phosphors 3.18 image scanner device that converts an analogue image into a digitized image with the desired resolution There are mainly two different types of scanners: flatbed type and drum type image sensor device, such as a charge-coupled device (CCD) array or complementary metal-oxide semiconductor (CMOS) sensor, that converts visual image information to an electric signal, built-in digital camera or other imaging devices 3.20 image wobbler deflection coil to change direction of incident electron beam onto the specimen This coil is activated in a periodic manner with the aim of identifying easily the place of focus just focus focusing condition in which the specimen height coincides with the object plane of the objective lens 3.22 lattice image image consisting of interference fringes formed by the interaction between the transmitted electron beam and diffracted electron beam from a specific crystal plane Lattice fringes can be used to calibrate image magnification at the high end of the magnification range. ISO 2010 All rights reserved 3

10 Provläsningsexemplar / Preview 3.23 lattice spacing crystallographic distance between two adjacent parallel planes with the same Miller indices, which can be calculated from the value of the basic cell vector 3.24 magnetic hysteresis physical phenomenon related to the magnetizing loop in which the magnetic field strength depends on the direction of the adjustment of the exciting current for the magnetic lens 3.25 optical axis straight line passing through the symmetrical centre of the magnetic field of the electron lens The path of an electron beam along this axis goes through the lens without changing the direction photographic film negative film sheet or a roll of thin plastic coated by photographic emulsion for recording an image 3.27 pixel-resolution number of imaging pixels per unit distance of the detector Typical unit is sometimes expressed as dots per inch (dpi) reference material RM material or substance, one or more of whose property values are sufficiently homogeneous and well established to be used for the calibration of an apparatus, the assessment of a measurement method, or for assigning values to materials For the purpose of this International Standard, an RM possesses periodic pattern(s) with the desired range of periodic interval and accuracy, to be used for the calibration of the image magnification region of Interest ROI a part region extracted from the whole area in the graph 3.30 specimen small portion of a sample for observation For TEM, a specimen has to be thin enough to transmit the electron beam specimen cartridge part of specimen holder which supports a specimen and is attached to the tip of the specimen holder for use 3.32 specimen drift unintentional movement of the specimen due to any source (thermal, mechanical, electric, charging) 4 ISO 2010 All rights reserved

11 3.33 specimen height specimen position along the optical axis of the objective lens 1 Specimen height = 0 corresponds to the specimen position in correct focus under the standard excitation condition of the objective lens. 2 See Reference [2] in the Bibliography specimen holder device that supports a specimen in the right position in the pole-piece gap of the objective lens 3.35 standard excitation condition optimal condition for excitation current of the objective lens to focus the image 1 This condition is provided by the TEM manufacturer for each instrument. 2 Image magnification is generally measured under this condition; however, as long as reproducible conditions are established, the magnification can be calibrated at any of the instrument settings super-lattice stable periodic structure which is fabricated by alternating layers of at least two different kinds of materials The super-lattice can be used as a reference material for calibration of image magnification from a mediumhigh to high magnification range transmission electron microscope TEM instrument that produces magnified images or diffraction patterns of the specimen by an electron beam which passes through the specimen and interacts with it 3.38 zone axis crystallographic direction, designated [u v w], defined by the intersection of a number of crystal planes (h 1,k 1,l 1 h i,k i,l i ) such that all of the planes satisfy the so-called Weiss zone law; hu + kv + lw = 0 4 Image magnification 4.1 Definition of the image magnification The image magnification (or scaling factor) of the TEM is defined by the ratio of the linear dimension of the specific structure on the detected image to the corresponding linear dimension of the specific structure in the specimen. There are three main kinds of image detectors: photographic film, imaging plate, and image sensor, such as CCD array or CMOS sensor built in the digital camera. In general, the value of image magnification detected on an image sensor is different from the value of image magnification detected on the photographic film or imaging plate under the same electron optical conditions for TEM imaging, because the image-detecting positions are different from each other (see Figure 1). ISO 2010 All rights reserved 5